Glycerine extraction process



J. C. ELGIN Aug. 16, 1949.

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traction of glycerine.

Patented Aug. 16, 1949 2,479,041 g GLYCERINE EXTRACTION PROCESS Joseph Clifton Elgin, Princeton, N. J.','assignor to- Colgate-Palmolive-Peet' Company, City, N. J a corporation or Delaware Jersey Application September 18, 1943, Serial No. 502,928

This invention relates to a method of treating water-soluble polyhydroxy organic materials in aqueous solutions containing the same and is a continuation-in-part of my application Serial Number 349,595, filed August 2, 1940, and now abandoned. More particularly the'invention relates to methods 'of purifying, concentrating, extracting and recovering polyhydric alcohols such as glycerine from aqueous solutions thereof. r

There have been vague suggestions in some patented art that glycerine may be purified by 19 Claims. (Cl; 260-637) means of organic solvents, and in other patents that the glycerine may be separated from associated materials by extraction. In most cases there is no detailed procedure for accomplishing these ends and, generally, the disclosed methods are'inoperative to attain the'described results. not dissolve either the glycerine or the water to a practical extent. Obviously, therefore, substantially no extraction, or practical separation Even though two liquid layers may result when contacting aqueous glycerine with such solvents, the ratio of glycerine to 'Water in the solvent is substantially the same as in the water and equal to that of the starting material. Furthermore, the concentration ofglycerine in the solvent is very small or negligible.- This, of course, does The solvents recited in many cases do erine remains absorbed, and subsequently dissolving out this glycerine from the solid residue with solvents, does not constitute separation of Water and glycerine or concentration of glycerine by liquid-liquid extraction; such a process is simple leaching and does not fall within the scope of this invention.

Even if some of the solvents disclosed inthe patented art were employed in liquid-liquid extraction they would be found to dissolve water in a higher ratio to glycerine than the ratio of these materials in the starting mixture. I Hence:

attempts to extract the glycerine into the solvent and recover. the glycerine therefrom would result in incomplete stripping, and the solvent .phase would contain a lower glycerine content not only in the solvent but 'on a solvent free basis, that'isa less concentrated aqueous glycerine solution. A process operated in this manner would generally be uneconomical.

It has now been discovered that relatively. concentrated, pure glycerine may be recovered from aqueous glycerine solutions by means of asol- -a liquid-liquid extraction with organic solvents not constitute a separation of glycerine and water, nor a concentration, purification or ex- Such a treatment is a simple dissolving of aqueous glycerine, and its continuation to the maximum limit possible would result solely in dissolving all ofthe starting mixture in the solvent thereby wholly defeating either the removal of glycerine from water, concentration of the glycerine or purification of the glycerine. Treating aqueous glycerine in such manner and with such solvents that only one liquid layer or phase is formed in the process, even though solids which may be contained therein be precipitated with the formation of a solid phase by the addition of sufficient solvent, likewise does not constitute a separation of water and glycerine, a concentration of glycerine, or

an extraction of glycerine in the sense of this invention. Such a process is simple solution of aqueous glycerine, is not a liquid-liquid extraction, and does not come within the scope' of this invention. Further, the evaporationof an aqueous glycerine mixture containing solids so that water is thus removed to leave a residue of solids in which a substantially dehydrated glycin two or more solvent extraction steps so thattwo liquid layers or-phases are formed in each of the steps in which the glycerine to [water ratios are substantially difierent from each other and from the original mixture of glycerine and 4 water. The glycerine may be concentrated and purified whether the glycerine to water ratio is higher or lower in the solvent phase than in the aqueous phase by the process of the tion of glycerine there is nearly/always a substantial quantity of water dissolved, in many cases in a higher ratio to the glycerine than-in the original'mixture, and the glycerine concentration in the total solution is nearly always lower than in the original mixture. In those cases where a water selective solvent is employed it is usually desirable to recover the concentrated glycerine from the aqueous phase, not the solvent phase.

The applicant is the first to concentrate glycerine in its aqueous mixture and to separate glycerine and water by liquid-liquid extraction with an organic solvent. The applicant is also the firstto observe that with certain solvents under certain conditions, there is a mixture, corresponding in principle to a constant boiling mixture in distillation, beyond which the particular solvent cannot eflectively extract without some change of extraction conditions. In other words, on one side of this composition the solvent such as tertiary amyl alcohol will selectively extract glycerine, on the other it will selectively extract water, and at the exact composition it is non-selective.

The process in general comprises extracting an aqueous mixture containing glycerine with an organic solvent under such conditions that two I liquid layers or phases are formed, one of which range now existing in the starting material, under such conditions that two liquid layers or phases are again formed, one of which liquid layers con tains glycerine in proportion to water substantially different from that which obtained in the mixture which served as a starting material for this second liquid-liquid solvent extraction. The result is thereby to remove the glycerine or water or both successively from the original mixture and thus concentrate the glycerine. That is, water may be first removed from the mixture in the extract phase leaving a more concentrated glycerine solution behind which may then be treated with a second solvent in the second stage of the process which preferentially takes glycerine into the extract phase and this extract when separated from the solvent will be a concentrated glycerine. No procedure described in the prior art does such a true glycerine extraction process.

The invention herein described also contemplates the liquid-liquid extraction of crude liquid aqueous glycerine mixtures containing in addition dissolved and/or suspended inorganic and/or organic impurities, such mixtures being derived from any source, for the purpose of obtaining an extracted glycerine of both higher concentration relative to water and containing substantially none or only small quantities of undesirable impurities, such as for example, inorganic compounds, salts and alkalies (e. g. sodium chloride, caustic soda, sodium carbonate and iron acetate), colored bodies, nitrogenous substances,

, organic salts and fatty acids. While it is usually desired to attain both objects, it is not intended to limit the invention thereto, since it may also be employed solely to concentrate an aqueous glycerine of any degree of purity by preferentially dissolving the water, or the glycerine, therefrom. Or, it may be applied solely for the purpose of extracting and stripping substantially completely-a glycerine of greater purity and having, for example, lower salts, caustic and color content, from an impure crude aqueous glycerine 4 mixture without necessarily eflectlng a concentration of glycerine thereby.

The invention may be applied to the extraction, purification, and concentration of glycerine in such aqueous mixtures as soap lyes, saponiflcation liquors, or other glycerine containing liquors derived from the hydrolysis of fats and oils in the manufacture of soap and fatty acids, mixtures obtained therefrom by evaporation or other treatment, e. g. crude concentrated glycerines;

fermentation liquors and slops derived from the fermentation of molasses or other carbohydrate containing material carried out either for the primary production of glycerine or for alcohols and similar substances; and of crude aqueous glycerine liquors derived synthetically, for example, by the chlorination of propylene and the subsequent hydrolysis or hydrinolysis of the chlorinated hydrocarbon. The process possesses particular merit for the purification of glycerine containing organic impurities having a boiling range near that of glycerine such as the glycerine obtained by distillation from fatty oil soaps e. g. by the process described in Ittners U. S. Patent Number 1,918,603 and Clayton et al.s U. S. Reissue Patent Number 19,456. Use of the invention is not, however, limited thereto. While it is proposed to extract usually the glycerine from its mixtures without prior chemical or adsorption treatment or evaporation thereof, it will be understood that chemical or adsorption treatment and/or artial concentration of such mixtures by evaporation or distillation prior to the extraction, so long as there remains a liquid phase; may be carried out without departing from the spirit of this invention. It is possible to employ chemical or adsorption treatment or concentration subsequent to the extraction. The concentration may be effected by any suitable method e. g. as described in Martin H. Ittners U. S. Patents Numbers 2,164,274; 2,164,275 and 2,164,276.

As previously described if dewatering of aqueous glycerine is the sole objective, the mixture may be extracted with a suitable solvent under such circumstances as fulfill the previously specified conditions so that either water or glycerine is preferentially dissolved by the organic solvent or solvent mixture used in the various steps of the process. In treating crude, highly colored, impure aqueous glycerines which are relatively dilute, that is with a glycerine content between a trace and 50%, it is preferred to separate the glycerine and water therein by extracting with such solvents and in such manner that glycerine is preferentially dissolved and concentrated in the organic solvent layer, thus leaving behind in the aqueous layer the major portion of the colored matter, inorganic substances and other impurities. The solvent solution of glycerine may have lower viscosity, surface tension and salt content than strong and/or crude glycerines and may be cleaned readily by means of absorbent carbon, activated carbon kieselguhr, silica gel or the like. As stated, it has been found in carryin out the extractions with solvents that the colored bodies, inorganic substances, and other imerentially water-soluble. Conversely, when ex tracting water from an aqueous glycerine solution in the first step of the process, it is often desirable to have an acid condition in order to favor the solution Of the organic impurities iii the solvent, leaving a purer non-solvent phase containing concentrated glycerine, inasmuch as the impurities, such as fatty acids, when acid tend to be dissolved preferentially in the solvent phase.

In the preparation of a highly concentrated glycerine from a crude glycerine mixture ithas been found particularly advantageous from an economicaland practical standpoint to carry out the extraction in .two or more distinct and successive steps in each of which is employed a different solvent. The solvent chosen'for each of the extraction steps should preferably be one which is best suited for operation with the particular concentration of the glycerine in the aqueous solution being treated in that step. It is of course necessary to select a solvent which will preferentially dissolve water or glycerine depending upon which it is most desirable to remove at the particular stage in the process then in progress. The applicant has found that certain solvents are more successful when used for extracting dilute aqueous glycerine solutions, that is less than 50% and more generally in the range from a trace up to 20 or 30%, whereas other solvents are best suited for extractin the concentrated glycerinesolutions, either by removing the remaining few percent of water, where the solvent is water selective, or by dissolving substantially pure glycerine only from the concentrated solution, where the solvent is glycerine selective. Generally speaking, the solvents which are most eflicient when Working upon the dilute glycerine solutions are fairly satisfactory for the solutions containing from 35 to 65% glycerine although some of the solvents which are very effective for the final purification are also suitable'for operation in this middle range of concentrations. It is also possible to use one solvent in the low range of glycerine concentration, a second solvent when the concentration approaches 50% and a third solvent for the final separation. For such an operation, as an example, one might use a water selective solvent with the mixture alkaline to first remove a considerable portion of the water and the impurities, then treat the mixture with a second, glycerine selective solvent which would take a concentrated glycerine solution into the extract phase and finally treat this concentrated glycerine solution with a third solvent, which might be either water selective, to remove the remaining water, or glycerine selective, to dissolve out a pure glycerine from this concentrated solution. It is of course possible and, in some cases, might be more economical to use 4 or even 5 or more extraction steps. However this would be unusual and only justified under extreme circumstances. As a general'rule a 2 or 3 step extraction process will prove most economical.

In place of the use of a solvent extraction step for concentrating in one of the steps of a 3 or more step process, it'might be advantageous to substitute a distillation operation to concentrate the solution up to the range desired for the next succeeding extraction step. This is particularly true in passing through the range from a'dilute glycerine solution containing 35% of glycerine or glycerine from the ramnate, when using a glycerine selective solvent in one of the stages of the process, isthat the raflinate maybe washed in a counter-current extraction process with a water selective solvent to such an extent, or in such a manner, that the glycerine-water ratio in the raflinate is the same or substantially the same as in the feed to the original extraction step. The ramnate may then be return'edfto the mixture being fed into the" extractor and re-extracted with the glycerine selective solvent. This feature is of particular advantage in conjunction with the final stages of the process in which the. glycerine content of the rafflnate from the extraction step may well be fairly large and have consider-# able value. By treating this rafllnate with a'wa ter selective solvent the material being removed from the process 'will' be mainly this water selective-solvent and the water being carried along therewith. The ramnate is continuously returned to the original counter-current extractor until its glycerine content has been substantially all removed in the extract phase with the glycerine selective solvent. Although this step of recovering the glycerine from the raflinate portion of an extraction step is preferably of advantage when dealing with aconcentrated glycerine solution, it may be used in any stage of the process where a glycerine selective solvent is used in the extraction and it is undesirable or uneconomical to use this glycerine selective solvent in a suflicient proportion to strip the feed to the extractor of its glycerine content. The mode of operation of such a railinate extraction step may be more fully understood by a study of the flow sheets of Figure 28 and Example 5.

In the investigations and extractions of aqueous glycerines, the following solvents have been found to be among those suitable for use in this invention: aliphatic alcohols containing more than two and preferably less than eight carbon atoms, e. g. n-, iso-, sec-, and tert.-butanols,

nand iso-propanol, methyl butanol, ethyl bu- T tanol, n-, iso-, sec and tertiary amyl alcohol, methyl amyl alcohol, hexanols; aromatic alcohol, e. g. benzyl alcohol; cyclic hydroxy compounds, e. g. cyclohexanol, methyl cyclohexanol, phenol, cresol, ortho amyl phenol, guaiacol; aliphatic, aromatic and cyclic amines, e. g. triethylamine (water miscible at low temperature, partially immiscible high temperature), aniline, quinoline, picolines; and ketones, e. g. acetone, methyl ethyl ketone (water miscible at very low and high temperatures, partially miscible at medium-temperatures), and methyl isobutyl ketone. It will be understood that the invention is not limited to those'solvents named, but that one may employ as solvent any organic liquid -which forms two liquid layers with the aqueous glycerine mixture, which results in one or the other of the liquid layers containing glycerine in ratio to water higher than the other layer or than the starting mixture, and which solvent, if mixed with eitherone or the other of the two pure components, glycerine or water, in the absence of the other, dissolves at least 4% of that component which itselectively extracts from tertiary mixtures with both of the components. Other solvents both of the above preferred class and of different classes, for example, certain ethers e. g. glycol monobutyl ether, dioxane, propylene oxide, diglycol monobutyl ether, mannitan, tetrahydrofurfuryl alcohol, furfuryl alcohol; certain esters e. g. monoacetin, diacetin, glycol monobutyrate, butyl lactate,n-propyl lactate and 

